Stable Isotope Profiles Research Articles

Fisheries shocks provide an opportunity to reveal multiple recruitment sources of sardine in the Sea of Japan

The abrupt decline in sardine catches in the Sea of Japan and the East China Sea (SJ-ECS) in 2014 and 2019 and the recovery in the following years call into question the current assumption that sardines in the SJ-ECS form a self-recruiting subpopulation. To test this hypothesis, we analysed otolith stable oxygen and carbon isotope profiles (δ18O, δ13C) of age-0 and age-1 sardines from 2010 and 2013–2015 year-classes captured in the SJ-ECS, as geographic markers for nursery areas. Age-0 sardines generally showed a significant ontogenetic decrease in otolith δ18O from larval to juvenile stages. However, the majority of age-1 captured in spring 2011, 2015 and 2016 showed non-decreasing otolith δ18O profiles, suggesting that the age-0 off the Japanese coast were not the main source of recruitment. Different migration groups were thus indicated: the “locals” growing up off the Japanese coast and the migrating “nonlocals”. The isotope profiles of the “nonlocals” overlapped with those of age-0 captured in the subarctic North Pacific, suggesting that they may be migrants from the Pacific, or perhaps an unobserved northward migration group in the SJ-ECS. Our results highlight the considerable uncertainty in the population structure assumed in current stock assessment models for Japanese sardine.

Individual isotopic niche variation of herbivores and palaeoenvironmental reconstruction of the Mid-Pleistocene Site of Kathu Pan 1 (South Africa)

Individual niche variation occurs when individuals within a population adopt unique behavioural or ecological traits, giving the population a distinct niche structure. Although widespread amongst natural populations, most of niche theory and its applications in ecological and palaeoenvironmental contexts remains focused on species level patterns, treating variation within the population as noise. Using serial stable isotope profiles sampled along teeth of herbivore fossils recovered from the Mid-Pleistocene site of Kathu Pan 1, Northern Cape (South Africa), enabling partitioning of isotopic niche variation into between- and within-individual components. Stable carbon isotope data revealed significant dietary differences between-individuals within most of the taxa sampled, but no dietary differences between taxa. By contrast, stable oxygen isotope compositions were more consistent amongst individuals, but varied across taxa. In both isotope systems, as well as in bivariate space, most taxa comprised individuals with both narrow and broad isotope niches, indicating flexibility in dietary strategies. These results indicate sufficient opportunity for individual level specialization within the Kathu palaeocommunity, afforded by a palaeoenvironment that provided a consistent supply of resources year-round. Given the herbivore sample is strongly associated with fossil hominin activities, our results imply that hominins in these landscapes would have profited from year-round accessibility to resources, accounting for the record of occupancy of Kathu Pan I during the Mid-Pleistocene.

Multi-disciplinary approach identifies pelagic nutrient linkage by sawsharks

Quantifying the trophic role of a species is key to understanding its ecology and ecological role. Their trophic role can influence community composition, ecosystem stability, and nutrient transport and cycling between habitats through ingestion, egestion, and excretion, which requires an understanding of species diet and habitat use. Despite the regular occurrence of sawsharks in Australian temperate fisheries, there remains limited information on their trophic ecology or habitat use, but they are assumed to be benthic consumers. We used fatty acid and stable isotope profiles along with stomach content analysis to investigate the trophic ecology of two sympatric species of sawsharks, the common sawshark (Pristiophorus cirratus) and southern sawshark (Pristiophorus nudipinnis) in south-eastern Australia. Stable isotope analysis of δ13C, δ15N, and δ34S in sawshark muscle revealed that P. nudipinnis fed at a higher trophic level than P. cirratus, and mixing models and stomach contents indicated P. nudipinnis was surprisingly reliant on pelagic and benthopelagic prey sources. In contrast, P. cirratus preyed on more benthic invertebrate species, not found in P. nudipinnis. This bentho-pelagic partitioning between species was supported by P. nudipinnis fatty acid profiles having higher levels of tracers associated with dinoflagellate basal sources (16:1/16:0, 22:6ω3) than P. cirratus, indicating a reliance on pelagic food webs. These data demonstrate that sawsharks are mesopredators that play a substantial role linking pelagic and benthic food webs and highlights the value of incorporating multiple biochemical tracers to provide a comprehensive representation of an animal’s trophic ecology and role in and between ecosystems.

Isotope-based inferences of the trophic niche of short-finned pilot whales in the Webbnesia

Knowledge of predator-prey interactions is key in ecological studies and understanding ecosystem function, yet this is still poorly explored in the deep-sea environment. Carbon (δ13C: 13C/12C) and nitrogen (δ15N: 15N/14N) stable isotope ratios of a deep-diving species, the short-finned pilot whale (Globicephala macrorhynchus), were used to explore knowledge gaps on its ecological niche and foraging habitats in the Webbnesia marine ecoregion (Tenerife Island, n = 27 animals vs. Madeira, n = 31; 500 km apart) where animals display distinct levels of site fidelity. Specifically, we tested whether intraspecific isotopic variation results from differences between geographic areas (due to possible foraging plasticity between regions), sexes, and/or years (2015–2020) using Generalized Linear Models. In general, significant differences (p < 0.05) were found in the stable isotope profiles of pilot whales between the two archipelagos, which were also reflected in their isotopic niche. The higher mean and wider range of δ15N values in Tenerife suggest that pilot whales consume prey of higher trophic levels and more diverse than Madeira. The higher mean and wider range of δ13C values in Madeira suggest that in that island, pilot whales rely on prey from more diverse habitats. There was significant variation between some years, but not between sexes. Finally, we discuss pilot whales' foraging strategies worldwide and infer the reliance on benthic or benthopelagic food sources in the Webbnesia.

Tackling the plastisphere: the single-cell Raman spectroscopy framework

Conventional bulk molecular approaches, often limited by their destructive nature and low spatial resolution, face challenges when probing the intricate dynamics of the plastisphere. Here, we outline a framework employing Raman spectroscopy combined with stable isotope profiling (SIP) to interrogate the physiological function of the plastisphere microbiome and track its evolutionary trajectories.

Characterizing water solubility of fresh and aged secondary organic aerosol in PM2.5 with the stable carbon isotope technique

Abstract. The investigation of the water-soluble characteristics of secondary organic carbon (SOC) is essential for a more comprehensive understanding of its climate effects. However, due to the limitations of the existing source apportionment methods, the water solubility of different types of SOC remains uncertain. This study analyzed stable carbon isotope and mass spectral signatures of total carbon (TC) and water-soluble organic carbon (WSOC) in ambient PM2.5 samples for 1 year and established stable carbon isotope profiles of fresh and aged SOC. Furthermore, a Bayesian stable isotope mixing (BSIM) model was employed to reveal the water solubility characteristics of fresh and aged SOC in a coastal megacity of China. WSOC was dominated by secondary sources, with fresh and aged SOC contributing 28.1 % and 45.2 %, respectively. Water-insoluble organic carbon (WIOC) was dominated by primary sources, to which fresh and aged SOC contributed 23.2 % and 13.4 %. We also found that the aging degree of SOC has considerable impacts on its water solubility due to the much higher water-soluble fraction of aged SOC (76.5 %) compared to fresh SOC (54.2 %). Findings of this study may provide a new perspective for further investigation of the hygroscopicity effects of SOC with different aging degrees on light extinction and climate change.

Co-habiting ants and silverfish display a converging feeding ecology

BackgroundVarious animal taxa have specialized to living with social hosts. Depending on their level of specialization, these symbiotic animals are characterized by distinct behavioural, chemical, and morphological traits that enable close heterospecific interactions. Despite its functional importance, our understanding of the feeding ecology of animals living with social hosts remains limited. We examined how host specialization of silverfish co-habiting with ants affects several components of their feeding ecology. We combined stable isotope profiling, feeding assays, phylogenetic reconstruction, and microbial community characterization of the Neoasterolepisma silverfish genus and a wider nicoletiid and lepismatid silverfish panel where divergent myrmecophilous lifestyles are observed.ResultsStable isotope profiling (δ13C and δ15N) showed that the isotopic niches of granivorous Messor ants and Messor-specialized Neoasterolepisma exhibit a remarkable overlap within an ant nest. Trophic experiments and gut dissections further supported that these specialized Neoasterolepisma silverfish transitioned to a diet that includes plant seeds. In contrast, the isotopic niches of generalist Neoasterolepisma silverfish and generalist nicoletiid silverfish were clearly different from their ant hosts within the shared nest environment. The impact of the myrmecophilous lifestyle on feeding ecology was also evident in the internal silverfish microbiome. Compared to generalists, Messor-specialists exhibited a higher bacterial density and a higher proportion of heterofermentative lactic acid bacteria. Moreover, the nest environment explained the infection profile (or the 16S rRNA genotypes) of Weissella bacteria in Messor-specialized silverfish and the ant hosts.ConclusionsTogether, we show that social hosts are important determinants for the feeding ecology of symbiotic animals and can induce diet convergence.

Stable isotope profiling and its potential applications to poultry sciences

Metabolomics is a bottom-up approach to studying metabolism in living cells, tissues, organoids, or even whole organisms. In conjunction with genomics and proteomics, it is a crucial tool for better understanding complex biological systems. In comparison to genomics or proteomics, metabolomics more directly reflects the phenotype since it encompasses events that occur downstream of gene expression. In the field of poultry or avian diseases, this method is now well established, although it could have more innovative applications in the future. For example, 13C-guided metabolomics and flux analysis could be used to identify biochemical pathways associated with heat or immune stress. It could also help to explore the effects of alternatives to antimicrobials on the intestinal health of poultry and their action on avian pathogens, including the mechanisms of resistance and persistence. In this review, we discuss some basic principles of metabolomics and its current and potential applications in poultry.

Interpreting life-history traits, seasonal cycles, and coastal climate from an intertidal mussel species: Insights from 9000 years of synthesized stable isotope data.

Understanding past coastal variability is valuable for contextualizing modern changes in coastal settings, yet existing Holocene paleoceanographic records for the North American Pacific Coast commonly originate from offshore marine sediments and may not represent the dynamic coastal environment. A potential archive of eastern Pacific Coast environmental variability is the intertidal mussel species Mytilus californianus. Archaeologists have collected copious stable isotopic (δ18O and δ13C) data from M. californianus shells to study human history at California's Channel Islands. When analyzed together, these isotopic data provide windows into 9000 years of Holocene isotopic variability and M. californianus life history. Here we synthesize over 6000 δ18O and δ13C data points from 13 published studies to investigate M. californianus shell isotopic variability across ontogenetic, geographic, seasonal, and millennial scales. Our analyses show that M. californianus may grow and record environmental information more irregularly than expected due to the competing influences of calcification, ontogeny, metabolism, and habitat. Stable isotope profiles with five or more subsamples per shell recorded environmental information ranging from seasonal to millennial scales, depending on the number of shells analyzed and the resolution of isotopic subsampling. Individual shell profiles contained seasonal cycles and an accurate inferred annual temperature range of ~ 5°C, although ontogenetic growth reduction obscured seasonal signals as organisms aged. Collectively, the mussel shell record reflected millennial-scale climate variability and an overall 0.52‰ depletion in δ18Oshell from 8800 BP to the present. The archive also revealed local-scale oceanographic variability in the form of a warmer coastal mainland δ18Oshell signal (-0.32‰) compared to a cooler offshore islands δ18Oshell signal (0.33‰). While M. californianus is a promising coastal archive, we emphasize the need for high-resolution subsampling from multiple individuals to disentangle impacts of calcification, metabolism, ontogeny, and habitat and more accurately infer environmental and biological patterns recorded by an intertidal species.

Profiling ephedrine/pseudoephedrine and methamphetamine synthesised from benzaldehyde, nitroethane and dimethyl carbonate

In previous work, a novel pathway for the synthesis of ephedrine/pseudoephedrine and methamphetamine using the precursors benzaldehyde, nitroethane and dimethyl carbonate was investigated, and an impurity profile presented. This paper presents chiral and stable isotope ratios of ephedrine/pseudoephedrine and methamphetamine synthesised by this pathway. Based on the chiral profile and the more negative δ13C (avg. –33.2‰) and more positive δ2H values, it is possible to distinguish ephedrine/pseudoephedrine and methamphetamine prepared from this pathway from those of “fully synthetic”, “semi-synthetic” or “natural” origin. The more positive δ2H values of methamphetamine from this pathway allowed for differentiation from methamphetamine produced from phenyl-2-propanone. It was noted, however, that the use of stable isotope profiling would likely be limited when a benzaldehyde source having a negative δ2H value was used as a precursor. Furthermore, the stable isotope values alone could not be used to differentiate from methamphetamine prepared by the Akabori-Momotani reaction, highlighting the need for combination with impurity profiling.

Stable isotope profiling of cigarettes assisted with chemometrics for authenticity determination

The battle against tobacco fraud presents a formidable challenge, given the global proliferation of imitation and counterfeit cigarettes. This not only inflicts economic losses on governments but also poses significant health risks due to the prevalence of these fraudulent products. This research delves into the application of stable isotopes (δ13C, δ15N, δ2H, and δ18O) and bio-elements (C% and N%) to discern the authenticity of various cigarette brands. Differences in brand origin notably impacted the δ15N and δ2H values. The assessment of cigarette authenticity, as well as the specific brands, unveiled maximum variances in the δ15N and δ2H values, underscoring their potential as robust discriminators between genuine and counterfeit products. Unsupervised Principal Component Analysis results consistently corroborated the authenticity of the samples for the four brands. The integration of chemometric methods, such as Orthogonal Partial Least Squares-Discriminant Analysis, yielded highly accurate authentication for cigarettes across the four brand categories, achieving an accuracy of over 96.8 %. Additionally, this investigation revealed that the critical determinants in distinguishing authentic cigarettes were the isotopic values of δ15N, C%, and δ18O. This work paves the way for a more convenient avenue for the classification of cigarette authenticity compared to untargeted analysis that need to a comprehensive set of chemical fingerprints.

Seeing further into the early steps of the endangered atlantic goliath grouper (Epinephelus itajara): Eye lenses high resolution isotopic profiles reveal ontogenetic trophic and habitat shifts

Estuarine mangroves are often considered nurseries for the Atlantic Goliath grouper juveniles. Yet, the contributions of different estuarine primary producers and habitats as sources of organic matter during early ontogenetic development remain unclear. Given the species’ critically endangered status and protection in Brazil, obtaining biological samples from recently settled recruits in estuaries is challenging. In this study, we leveraged a local partnership with fishers and used stable isotope (C and N) profiles from the eye lenses of stranded individuals or incidentally caught by fishery to reconstruct the trophic and habitat changes of small juveniles. The eye lens grows by the apposition of protein-rich layers. Once these layers are formed, they become inert, allowing to make inferences on the trophic ecology and habitat use along the development of the individual until its capture. We used correlations between fish size and the entire eye lens size, along with estuarine baselines, to reconstruct the fish size and trophic positions for each of the lens layers obtained. We then used dominant primary producers and basal sources from mangrove sheltered, exposed estuarine and marine habitats to construct an ontogenetic model of trophic and habitat support changes since maternal origins. Our model revealed marine support before the juveniles reached 25 mm (standard length), followed by a rapid increase in reliance on mangrove sheltered sources, coinciding with the expected size at settlement. After reaching 60 mm, individuals began to show variability. Some remained primarily supported by the mangrove sheltered area, while others shifted to rely more on the exposed estuarine area around 150 mm. Our findings indicate that while mangroves are critical for settlement, as Goliath grouper juveniles grow, they can utilize organic matter produced throughout the estuary. This underscores the need for conservation strategies that focus on seascape connectivity, as protecting just one discrete habitat may not be sufficient to preserve this endangered species and safeguard its ecosystem functions.

Estimating whisker growth rates and foraging profiles for northern fur seal pups and adult females using stable isotope analysis

Changing ratios of stable carbon ( δ13C) and nitrogen ( δ15N) isotopes in consumer tissues reflect foraging patterns over time and can be used to inform studies on historically vulnerable populations. Northern fur seals (NFS; Callorhinus ursinus) at San Miguel Island (SMI), California, have been severely impacted by climate events such as El Niño and remain susceptible to future environmental disturbances, necessitating the need to further understand their foraging ecology. We analyzed sequential δ13C and δ15N values along single NFS whiskers sampled from five pups and five unrelated post-parturient females at SMI and reconstructed temporally aligned stable isotope profiles for each whisker. Pup profiles consistently showed increases in postnatal δ13C and δ15N values that likely stem from pup consumption of maternal milk and changes in maternal foraging locations after parturition. Adult female profiles indicated predominantly heterogeneous foraging strategies and minimal foraging outside the Southern California Bight. These findings provide initial characterizations of longitudinal, stable isotope-derived foraging data for NFS from SMI and offer insight into the inference of otariid foraging ecology with sequential δ13C and δ15N values.

Spatial, Seasonal, and Diel Controls of Nitrogen‐Carbon‐Oxygen Cycling During Lake‐Water Infiltration to an Aquifer

AbstractMany freshwater lakes are groundwater flow‐through systems. Although lakes commonly are considered to be sinks for nitrogen inputs, relatively little is known about carbon and nitrogen export from lakes to groundwater. The current study focused on lake‐bottom biogeochemical processes accompanying the transport of nitrogen, dissolved oxygen (O2), and dissolved organic carbon (DOC) during lake‐water recharge from a groundwater flow‐through lake. Lake‐water and porewater (15–100 cm below lakebed) samples were collected along transects within the lake downwelling zone. Infiltrating porewater O2 and DOC concentrations decreased with depth while nitrate (NO3−) concentrations increased, indicating nitrification of organic matter within the profiles. The depth of NO3− production and transport was seasonally dependent. In winter, NO3− and O2 were exported beyond 100‐cm depth; whereas in summer, shallow nitrification zones were underlain by deeper NO3− reduction zones, and diel patterns of O2 and NO3− penetration depths were observed. Microbial community compositions and stable isotope profiles (δ15N[NO3−], δ18O[NO3−], δ18O[O2]) were consistent with apparent C–N–O reaction stoichiometries indicating O2 reduction and nitrification in shallower porewater, followed by varying NO3− reduction at depth. Maximum porewater NO3− concentrations (∼10–20 μM) were limited by infiltrating O2 concentrations and C/N ratios of reacting organic matter. Lake‐water level variations caused changes in shoreline position and porewater velocities, while variations in lake‐water temperature, DOC, and O2 contributed to changes in reaction rates and depth of O2 and NO3− penetration into the lakebed. The quality of groundwater recharged by lake water reflected temporally and spatially varying physical and biogeochemical processes in the sediment porewater.

Geographical origin identification of Pujiang Kyoho grapes in China using stable isotope and elemental profiles

Grapes are an important seasonal fresh fruit in China, and their quality and nutrition is closely linked to their geographical origin. Stable isotopes and elemental profiles of grapes and corresponding soils from different regions and harvest years were determined using isotope ratio mass spectrometry (IRMS) and inductively coupled plasma mass spectrometry (ICP-MS). Results showed that stable isotope ratios and most elemental contents of grapes were significantly correlated to distinct regions and different harvest years. Na, Li, V, Co, Ni and Pb contents of grapes and corresponding soils were positively correlated, while Mg, Cu, Rb and Sr were negatively correlated (p < 0.05). A supervised chemometric model (random forest) was used to discriminate PGI Pujiang grapes from four other grape producing regions with 100% accuracy. These findings confirm that stable isotopes and multi-elements combined with chemometric analysis can effectively improve the accuracy of grape origin identification and minimize fraudulent mislabeling.

Stable isotope profiling of farmed Penaeus monodon for the evaluation of feed efficiency

AbstractThe current study profiled the dual isotopes of carbon and nitrogen in feeds and muscles of farmed Penaeus monodon for evaluation of feed efficiency in making up the prawn muscle. Signatures of both feed and resulted muscles of P. monodon were subjected to two‐ and three‐source linear mixing models to elucidate the contribution of each feed item in the building of the muscle. The results revealed that carbon and nitrogen in different feed substances have different influences on the growth and nutrient uptake by the prawn. Different growth stages showed isotopic switching within prawn muscles in the course of their building up. Generally, marine sources were the most enriched in both δ13C and δ15N. Likewise, δ13C of wild‐caught prawns (−16.30 ± 0.72‰) were superior over farmed prawns (−18.00 ± 0.59‰) (p &lt; 0.01), whereas no significant differences were observed in δ15N values between wild (8.03 ± 0.65‰) and farmed (8.38 ± 1.39‰) (p &gt; 0.01). The isotopic composition of P. monodon mirrored those of the ingredients contained in its feed and varied across treatment levels. Comparing to other ingredients, marine macroalgae exhibited significantly higher (p &lt; 0.01) feed efficiency, and as a result, they improved the growth of P. monodon compared to the other ingredients. The same treatment recorded significantly lower (p &lt; 0.01) feed conversion ratio compared to other treatments. However, muscle somatic index, specific growth rate and condition factor were not significantly different across treatments (p &gt; 0.01). Moreover, a clear distinction was observed between wild and farmed P. monodon, and such a distinction is clearly explained by δ13C composition. In conclusion, multiple sources of δ13C and δ15N in feeds are incorporated more efficiently in muscles than single sources.

Brazil Margin Stable Isotope Profiles for the Last Glacial Cycle: Implications for Watermass Geometry and Oceanic Carbon Storage

AbstractVertical profiles of benthic foraminiferal oxygen and carbon isotopes (δ18O and δ13C) imply the volume of southern source water (SSW) in the Atlantic basin expanded during the Last Glacial Maximum. Shoaling of the boundary between SSW and northern source water (NSW) may reduce mixing between the two watermasses, thereby isolating SSW and enhancing its ability to store carbon during glacial intervals. Here we test this hypothesis using profiles of δ18O and δ13C from the Brazil Margin spanning the last glacial cycle (0–150 ka). Shoaling of the SSW‐NSW boundary occurred during Marine Isotope Stage (MIS) 2, 4, and 6, consistent with expansion of SSW and greater carbon sequestration in the abyss. But the watermass boundary also shoaled during MIS 5e, when atmospheric CO2 levels were comparable to MIS 1. Additionally, we find there was little change in watermass structure across the MIS 5e‐d transition, the first major decline in CO2 of the last glacial cycle. Thus, the overall pattern in glacial‐interglacial geometry is inconsistent with watermass mixing acting as a primary control on atmospheric pCO2. We also find that δ13C values for MIS 5e are systematically lower than MIS 1, with the largest difference (∼1‰) occurring in the upper water column. Low δ13C during MIS 5e was most likely due to a long‐term imbalance in weathering and deposition of calcium carbonate or input of 13C‐depleted carbon from a reservoir external to the ocean‐atmosphere system.

The association between haemosporidian infection and non-breeding moult location in great reed warblers revisited by combining feather stable isotope profiles and geolocator data

Stable isotope analysis provides valuable insights into the ecology of long-distance migratory birds during periods spent away from a specific study site. In a previous study, Swedish great reed warblers (Acrocephalus arundinaceus) infected with haemosporidian parasites differed in feather isotope ratios compared to non-infected birds, suggesting that infected and non-infected birds spent the non-breeding season in different locations or habitats. Here, we use a novel dataset comprising geolocator data, isotopes, and haemosporidian infection status of 92 individuals from four Eurasian populations to investigate whether parasite transmission varies with geography or habitats. We found that the probability of harbouring Plasmodium and Leucocytozoon parasites was higher in birds moulting in the eastern region of the non-breeding grounds. However, no geographic pattern occurred for Haemoproteus infections or overall infection status. In contrast to the previous study, we did not find any relationship between feather isotope ratios and overall haemosporidian infection for the entire current dataset. Plasmodium-infected birds had lower feather δ15N values indicating that they occupied more mesic habitats. Leucocytozoon-infected birds had higher feather δ34S values suggesting more coastal sites or wetlands with anoxic sulphate reduction. As the composition and prevalence of haemosporidian parasites differed between the old and the current dataset, we suggest that the differences might be a consequence of temporal dynamics of haemosporidian parasites. Our results emphasize the importance of replicating studies conducted on a single population over a restricted time period, as the patterns can become more complex for data from wider geographical areas and different time periods.

Towards unlocking the trophic roles of rarely encountered squid: Opportunistic samples of Taningia danae and a Chiroteuthis aff. veranii reveal that the Southern Ocean top predators are nutrient links connecting deep-sea and shelf-slope environments

Deep-sea squids are presumably vital components of largely undescribed marine ecosystems, yet limited access to specimens has hampered efforts to detail their ecological roles as predators and preys. Biochemical techniques such as stable isotope analyses, fatty acid analyses, and bomb calorimetry are increasingly recognized for their ability to infer trophic ecology and dietary information from small quantities of tissue. This study used five opportunistically collected Taningia danae specimens and one Chiroteuthis aff. veranii specimen retrieved from the Great Australian Bight, South Australia, to detail the trophic ecology of these poorly understood squids. Four body tissue types (i.e., arm, buccal mass, mantle, and digestive gland) were assessed for their utility in stable isotope (SI) and fatty acid (FA) analyses, and we found that the arm, buccal mass, and mantle tissues had similar SI and FA profiles, suggesting that they can be used interchangeably when the entire specimen is unavailable. δ13C, δ15N, and fatty acid data suggests that the T. danae and C. aff. veranii specimens lived in the Southern Ocean and were high-trophic-level predators, feeding on deep-sea fishes and small squids, while also taking advantage of the summer upwelling region of the Great Australian Bight. The fatty acid analysis and bomb calorimetry results indicate that these squids might be important reservoirs of essential FAs (EPA and DHA) for Southern Ocean predators and that the whole-body energy content of T. danae individuals can reach up to 362,250 kJ. Our findings indicate that these squids may be contributing greatly to the transport of nutrients and energy between the Southern Ocean deep-sea and the Great Australian Bight shelf–slope environments. In addition to building our understanding of the trophic ecology of two poorly understood deep-sea squids, these findings also highlight the utility of partial specimens and demonstrate the important ecological information that can be obtained from few samples that may be opportunistically collected.

A comparison of stable isotopes and polychlorinated biphenyls among genetic strains of Lake Ontario lake trout (Salvelinus namaycush)

This study quantified stable carbon (δ13C) and nitrogen (δ15N) isotopes, polychlorinated biphenyl (PCB) concentrations and growth rates among multiple genetic strains of Lake Ontario lake trout (Salvelinus namaycush) to evaluate the potential role of genetics in these parameters. Fish ranging in age from 1 to 31 years (n = 72) and representing nine genetic strains including wild-recruits to hatchery fish derived from Lakes Ontario, Superior and Champlain watersheds, and individuals of unknown hatchery origin. Carbon (δ13C) and nitrogen (δ15N) stable isotope values averaged −22.2 ‰ and 17.4 ‰, respectively, but did not differ significantly among genetic strains. ΣPCB concentrations ranged from 42 to 1820 ng/g and varied significantly among individuals including those of similar age and genetic strain. For example, Sum PCB (ΣPCB) concentrations among 7-year-old fish (n = 16) ranged from 159 to 607 ng/g, which compares to growth rates of 3.5 – 32.9 %/yr for these same fish. Multivariate analysis of stable isotope and PCB profiles, however, provided considerable resolution among the strains. For example, fish of unknown hatchery origin ordinated most similar to Seneca Lake fish, the predominant strain stocked in Lake Ontario. Wild fish had a unique ordination with only Lake Superior Klondike strain fish overlapping into their ordination space. Lakes Champlain and Superior strain individuals had similar ordinations but did not overlap substantially with wild or Klondike strain fish. Combined, these differences agree with the ecologies described for these strains in their native ecosystems suggesting that insight can be gained from strain specific evaluations of ecological tracers and these pollutants among Great Lakes lake trout.